BRITISH AVONIAN CONODONT FAUNAS 63 
nathus beckmanm—Gnathodus bilineatus Zone appears to be at the base of the Cu III 8 
Zone, the zone being confined to Cu III «. 
The fauna resembles that of the St. Louis Limestone, and has a very close similarity 
to that of the overlying St. Genevieve Formation. 
The base of Dg in the Avonian is within the Gnathodus bilineatus—Cavusgnathus 
charactus Assemblage Zone of North America. G. bilineatus first appears in the base 
of this zone in the Mississippi Valley, but the details of this North American zone are 
not yet fully studied (Collinson, Scott & Rexroad 1962 : 25). The species first 
appears in the higher part (Unit C) of the Pella Formation of Iowa (Rexroad & 
Furnish 1964). 
One anomalous aspect of this correlation is the reported first appearance of the 
Gnathodus girtyt group at the top of this zone in the Mississippi Valley (Collinson, 
Scott & Rexroad 1962 : 25). 
The Gnathodus mononodosus Zone includes the last appearance of M. beckmannz, 
which is last found in the Middle Cu III 8 of Germany (Meischner 1962). The fact 
that our zone is established on the basis of a new species makes more precise correla- 
tion difficult. G. nodosus, which first appears at the base of this zone in the North 
Crop, first appears in the Middle Cu III 8 zone of Germany (Meischner 1962). 
The overlying Gnathodus girtyi collinsoni Zone represents the first appearance of 
G. girtyi collinsom (= G. girtyi Form C of Meischner 1962), which first appears at the 
base of Cu III y, in the Middle Rhenaer Kalk of Germany. The last appearance of G. 
_ homopunctatus on the North Crop falls within this zone, and this is closely similar to 
its last appearance in Germany (Meischner 1962 : 31, Chart 10). The overall aspect 
of this Avonian Zone is similar to that of the pre-Middle Glen Dean Chesterian 
Formations of the Mississippi Valley. 
(i) France and Belgium 
There are no adequately illustrated accounts of the Lower Carboniferous faunas of 
France or Belgium, and our comparisons are made on the basis of published faunal 
lists. We have not been able to study the original specimens, and our correlations 
are, therefore, tentative and provisional. 
: Conil, Lys & Mauvier (1964) have studied the conodont faunas of the Tournaisian 
: and Viséan in Belgium and France. They showed that Taphrognathus (synonymous 
with Patrognathus gen. nov. or Clydagnathus gen. nov.) occurs in beds that are of 
| Tnj,-Ing, age. Associated with Taphrognathus in Tnyp are Polygnathus inor- 
natus, Pseudopolygnathus dentilineatus, Elictognathus costatus and Siphonodella 
_obsoleta, a fauna which is closely similar to that of the Upper K Zone. In Tngp 
Siphonodella duplicata, Siphonodella lobata and Siphonodella quadruplicata appear, 
whilst in Tn. Siphonodella sexplicata makes its first appearance. 
Tn. is characterized by the presence of the genera Pseudopolygnathus, Siphono- 
della and Elictognathus. The base of Tng, would appear to correlate with the upper 
part of the Middle Hannibal Formation of North America, based on the first occur- 
rence of the species Siphonodella cooper and Siphonodella sexplicata. 
At the base of Tn3, in Belgium and France, the following species have their first 
